1. Field of the Invention
The present invention relates to a tilt-type steering device and more particularly to a column mounting assembly for a tilt-type steering device capable of adjusting the height position of a steering wheel to a driver's physique and posture during driving.
2. Related Background Art
A tilt-type steering device can adjust the height of a steering wheel freely by supporting a portion of a steering column raisably and lowerably relative to an automobile body. The intermediate portion of the steering column constituting such a tilt-type steering device is supported by the body via, e.g., a structure as shown in FIGS. 2 and 3 in a lower surface portion of a dashboard or the like. A supporting bracket 1 constituting this supporting device is made of one piece by subjecting a steel plate with sufficient rigidity to press working, and has a pair of lateral vertical plate portions 2a, 2b provided so as to have a certain distance between them and mounting plate portions 3a, 3b formed on the upper portions of the vertical plate portions 2a, 2b. In FIGS. 2 and 3 lower edges of the vertical plate portions 2a, 2b are connected by a connecting plate portion 4. Also, holes 5a, 5b are formed in respectively opposite positions of the vertical plate portions 2a, 2b so as to be elongated in the vertical direction.
Also, a raising and lowering bracket 7 is secured to the lower surface of the intermediate portion of the cylindrical steering column 6 between the pair of the vertical plate portions 2a, 2b by means of welding. The raising and lowering bracket 7 is formed with a pair of lateral round holes 9a, 9b in opposition to the respective elongated holes 5a, 5b. A steering shaft 8 to be rotated by a steering wheel (not shown) is supported only rotatably inside the steering column 6.
A tilt adjusting bolt 10 is inserted in the elongated holes 5a, 5b and the round holes 9a, 9b. A tilt adjusting nut 11 is engaged with a male screw portion of an end portion of the bolt 10 projecting from the outer side surface of the vertical plate portion 2a (on the left in FIG. 3). Further, on the nut 11 is secured a base end portion of a tilt adjusting operation lever 12. A head 13 of the tilt adjusting bolt 10 and both side edges of the right-hand elongated hole 5b are engaged with each other so as to prevent rotation of the head 13, thereby constituting rotation preventing means for preventing rotation of the tilt adjusting bolt 10. Therefore, the head 13 is provided with flat faces 13a for contact with both side edges of the elongated hole 5b. Accordingly, when the operation lever 12 is operated, the distance between the head 13 and the tilt adjusting nut 11 can be adjusted.
For example, first, the operation lever 12 is rotated clockwise in FIG. 2, i.e., up to the position as indicated in phantom to enlarge the distance between the head 13 and the nut 11. Then, in this condition, when the bolt 10 is shifted along the elongated holes 5a, 5b to raise or lower the steering column 6, the height position of the steering wheel can be adjusted. On the other hand, when the operation lever 12 is rotated up to the position as indicated by the solid line of FIG. 2 thereby to shorten the above-mentioned distance, the raising and lowering of the steering column 6 is prevented and the height position of the steering wheel can be set to the position after the adjustment.
Under a portion of the rear end portion (right end portion in FIG. 2) of the steering column 6 projecting further rearward (rightward in FIG. 2) beyond the supporting bracket 1, a knee protecting plate 14 is secured, whereby driver's knees are prevented from colliding with square portions such as corners of the supporting bracket 1, etc. at the time of a collision accident. A crank-like bent portion 15 is provided in the intermediate portion of the operation lever 12 to avoid interference with the knee protecting plate 14. Also, the base end portion of the operation lever 12 is provided with a claw 16 for limiting the amount of rotation of the lever 12. The rotation range of the operation lever 12 is limited between the solid-line condition and the two-dot chain line condition by the abutting between the claw 16 and the rear end edge (right end edge of FIG. 2) of the vertical plate portion 2a.
Although the amount of rotation of the operation lever 12 is limited in accordance with the abutting between the claw 16 and the vertical plate portion 2a, the tilt-type steering device is assembled in the following manner such that the fastening and unfastening of the steering column 6 can be performed within the limited rotation range. First, the raising and lowering bracket 7 secured to the steering column 6 is inserted between the vertical plate portions 2a, 2b of the supporting bracket 1, and the tilt adjusting bolt 10 is passed through the elongated holes 5a, 5b of the respective vertical plate portions 2a, 2b and the round holes 9a, 9b of the raising and lowering bracket 7. Then, the head 13 of the bolt 10 is engaged with one elongated hole 5b (on the right side in FIG. 3), and the tilt adjusting nut 11 is engaged with the male screw portion provided on an end portion of the bolt 10. As the peripheral surface of the base portion (on the right side in FIG. 3) of the nut 11 is provided with a pair of flat faces in parallel with each other, the nut 11 is rotated by engaging a tool such as a spanner with the flat faces to shorten the distance between the nut 11 and the head 13, whereby the raising and lowering bracket 7 is secured to the supporting bracket 1.
After the raising and lowering bracket 7 is secured to the supporting bracket 1, a tapered tube portion 18 formed in the base end portion of the operation lever 12 is fitted on a tapered portion 17 formed on a half portion (left half portion in FIG. 3) of the nut 11. Then, the lever 12 is rotated to be in the solid line condition of FIG. 2. Next, a fixing screw 19 is fastened to the nut 11 via a washer 21 to secure the operation lever 12 and the nut 11. As a result, when the operation lever 12 is rotated until the claw 16 abuts onto the rear end edge of the vertical plate portion 2a, the raising and lowering bracket 7 is secured to the supporting bracket 1.
Although a drawing is omitted, there is a well-known structure in which a tilt adjusting nut is engaged with an elongated hole only raisably (not rotatably) and a tilt adjusting bolt is made rotatable.
In such a structure, the base end portion of a tilt adjusting operation lever is secured to the head of the bolt. Therefore, the head of the bolt is provided with a tapered portion and a screw hole for engagement with a fixing screw.
In the above-structured conventional tilt-type steering device, the material usable for the operation lever 12 is limited and it is difficult to form it lightly and cheaply. That is, in order to secure the operation lever 12 firmly to the tilt adjusting nut 11 (so as not to cause relative rotation), it is necessary to fasten the fixing screw 19 with a sufficiently large torque. As a result, a large amount of stress is applied to the tapered tube portion 18 formed in the base end portion of the operation lever 12. Therefore, the material for the operation lever 12 is necessitated not to be damaged by such stress and is steel conventionally. For forming the operation lever 12 lightly and cheaply, it is considered to utilize synthetic resin, aluminum alloy or the like. However, in the conventional structure shown in FIGS. 2 and 3, it is difficult to adopt these materials.
Also, there is considerable difference in temperature inside the automobile provided with the tilt adjusting nut 11 and the operation lever 12 between summer and winter. If the operation lever 12 is made of synthetic resin or aluminum alloy according to the conventional structure shown in FIGS. 2 and 3, there is a possibility that the contact pressure between the outer peripheral surface of the tapered portion 17 and the inner peripheral surface of the tapered tube portion 18 is changed beyond a permissible value due to the difference in thermal expansion between the steel adjusting nut 11 and the operation lever 12 based on the temperature difference. Then, if the contact pressure becomes excessively large, the tapered tube portion 18 may be damaged. On the other hand, if it becomes excessively small, the adjusting nut 11 cannot be rotated by the operation lever 12.
In Japanese Utility Model Publication No. 62-18121, another structure is described wherein an adjusting nut is linked to a base end portion of an operation lever by serration engagement. In the structure of this publication, there occurs no inadequate rotation of the adjusting nut by means of the operation lever depending on the temperature change. However, in the structure, the base end portion of the operation lever is also held tightly with a washer and the adjusting nut, so that a large amount of stress is added to the base end portion of the operation lever (particularly at the time of temperature rise). Therefore, it is difficult to make the operation lever by the use of synthetic resin or aluminum alloy.